package com.dyz.leetcode._12_linkedList;

import com.dyz.leetcode.ListNode;

import java.util.List;

public class _21_mergeTwoLists {
    public ListNode mergeTwoLists(ListNode list1, ListNode list2) {
        if(list1==null){
            return list2;
        }
        if(list2==null){
            return list1;
        }
        ListNode l1 = list1;
        ListNode l2 =list2;

        ListNode dummy = new ListNode(-1);
        ListNode curr = dummy;

        while (l1!=null &&l2!=null){
            if(l1.val<l2.val){
                curr.next = l1;
                l1 = l1.next;
            }else {
                curr.next = l2;
                l2 = l2.next;
            }
            curr = curr.next;
        }
        if(l1==null){curr.next = l2;}
        if(l2==null){curr.next = l1;}
        return dummy.next;
    }

    // 递归解法
    public ListNode mergeTwoLists2(ListNode l1, ListNode l2) {
        if (l1 == null) {return l2;}
        if (l2 == null) {return l1;}

        if (l1.val <= l2.val) {
            l1.next = mergeTwoLists(l1.next, l2);
            return l1;
        } else {
            l2.next = mergeTwoLists(l1, l2.next);
            return l2;
        }
    }
}
